The present invention is directed to a process for bonding wires to surfaces, for example, to form electronic device probes, or to form electrical connections on electronic circuit devices and particularly to wires that are bonded at one end with the other end free.
Wire bonding techniques were first developed back in the 1950""s for connecting germanium transistors to other electronic devices. Wire bonding techniques continue to be used for the vast majority of integrated circuit device connections. Thermal energy, mechanical force and ultrasonic vibrations are used to bond the tiny wires to the device terminals.
The Angled Flying Lead (AFL) wire bonding process disclosed herein uses the same basic processes that are used for a standard thermosonic ball bonding operation and it was developed for fabricating a variety of area array and peripheral interconnections including high density land grid array connectors and high density IC probes.
In conventional wire bonding, schematically shown in FIG. 1, a free end of a wire is ball bonded to a contact pad on a surface. The wire is bent over and wedge bonded to another pad. The wire joining the two pads is curved. The shape of the curve is determined by the distance between the two pads which are joined. If the wire joining the two pads are severed, two wires having different shapes are formed. If it is desired that the wires bonded to the surface be used as an electronic device probe (as described herein) or to interconnect an array of contact pads on a first surface to another array of contact pads on a second surface which is facing the first surface, the conventional wire bonding process is not useful to fabricate such structures. To fabricate a probe for an electronic device using wires (probe wires) bonded to a surface, one end of the wire is bonded to contact pads on a support substrate for the probe wires. The other ends of the probe wires must be positioned so as to be able to contact the contact pads on device being tested. When an electronic device probe is moved into engagement with the contact pads of the device under test, the probe wires preferably flex so that the free end (probe tip) of the wires wipe across the surface of the contact pad being probed. The wiping action permits the probe tip to make good electrical contact to a contact pad. Since a probe is used many times, the probe tips of the probe wires make many thousands (preferably greater than 1000, more preferably greater than 10,000, most preferably greater than 100,000) engagements and disengagements with contact pads on devices under test resulting in many repeated bendings. The probe tip also must be flexible enough to achieve the desired degree of wiping, withstand many engagements without deforming and be sufficiently compressible to without deformation. Applicants invention provides a method and approach which can reliable form many probe wires to a desired predetermined shape to satisfy all these requirements.
There is a need for a technique to form wires bonded to surfaces where the wires can be formed to have any desired shape to provide certain desired properties. The wires can be bonded to electrical contact pads on a surface drawn away from the surface and cut to have a free end. The wires are bent so that the free ends are placed in a predetermined shape which provide advantageous properties, such as a desired flexibility.
It is the object of the present invention to provide a process for bonding wires to an electronic circuit device with one end of the wire attached to the surface of the device and the other end of the wire extending away from the surface of the device.
Another object of the present invention is to provide a process for bonding wires to an electronic circuit device with the wires formed at an angle to the surface of the device.
A further object of the present invention is to provide a process for bonding wires to an electronic circuit device with the wires having curved features.